A Ca++-dependent secretion of norepinephrine ((3H)NE) was evoked in adrenergic nerves in rat heart ventricle slices incubated in a modified Krebs-HC03 medium containing choline C1 as the replacement for NaCl (Ch+ -Ca++). Exogenous ATP inhibited secretion, suggesting that the nucleotide stimulated a rapid uptake of (3H)NE in vesicles proximate to the axolemma. Lithium+ ion, a known inhibitor of NE uptake dependent upon Mg++ -ATPase activity in vesicles (but not ouabain), prevented the response to ATP in axoplasmic vesicles (Bogdanski 1983, 1986). This report indicates that other known inhibitors of uptake in isolated vesicles also inhibits the response to ATP in axoplasmic vesicles. Included were the inhibitors of Mg++- ATPase activity N-ethylmaleimide (NEM) and dicyclohexylcarbodiimide (DCCD) and the proton transporters 2,4- dinitrophenol (2,4-DNP 1.0 mM) and chlorpromaxine (CPZ). Potassium ionophores (valinomycin and 2,4-DNP0.1 mM, and nigericin) a carrier blocker (reserpine) and apH neutralizing reagent for vesicles (NH3 from ammonium sulfate in solution) were also effective. The inhibitors also increased the rate of depletion of stored NE and its deamination in nonsecreting nerve endings incubated in Krebs-HC03 (KRB) medium. Valinomycin stimulated uptake in the presence of ATP. It is suggested that mechanisms of uptake of NE in isolated vesicles apply to the axoplasmic vesicles as well. Thus, the activity of Mg++-ATPase drives proton transport to establish the electrochemical gradients of H+ which drive the transport of NE. Isolated adrenal medullary vesicles in the presence of ATP and Cl translocate a sufficient number of ions to establish a pH gradient and eventually cause osmotic lysis of the vesicle. By contrast exocytosis in axoplasmic vesicles was not apparent biochemically.